Transcript
Phil
Welcome to Board Talk. This is Jim Hall and Phil Zarrow, the Assembly Brothers, pick and place.
Jim
Also known as mild-mannered consultants for ITM Consulting.
Phil
And probably known as a few other things too, but, you know, this is a family program. We're coming to you from high atop Mt. Rialto, Board Talk Headquarters in Durham, New Hampshire. And what area of question do we have today?
Jim
This is about reflow of through hole, or if you like, pin-in-paste, or pin-in-hole, or intrusive soldering. Whatever you wish to call this technique. And the question comes from Madolfo in Canada.
I have this USB four pin connector using a pin-in-paste process in one of our high runner boards." High runner means large volume manufacturing I assume. I just noticed it today after 1200 boards that the solder paste being pushed out of the four pins at the bottom side is dripping and accumulating inside our oven.
Mostly on the second and third zones whose temperatures are operating at 120 and 140C respectively in a 12 zone oven. The question is, Is this normal, or what is normal inside the oven for pin-in-paste process? The protrusions of the four pins at the bottom side is 1 millimeter or 40 mils.
Phil
The first question, "What's normal?" I don't know what's normal. But we won't get philosophical here. I think one of the key problems here is the protrusion of your leads below the board being .040" is probably excessive. If it's at all possible, it would be best to acquire the connectors or pre-trim them to a maximum of .030" to alleviate the dripping problem.
The other question to ask yourself, assuming you put up with the tidiness question here with regard to the dripping solder, "What do the joints look like?" Are you losing solder volume?
Jim
What is your hole fill ratio?
Phil
That's right. Are you filling the hole? What do the fillets look like? Knowing that, you don't necessarily have to have a positive fillet on either side. That's been proven. But are you getting antiquate joints? So, if you can live with the sloppiness factor I guess you could say, that's fine, but ideally you want to limit that protrusion to between .020" and .030" below the lower surface of the board.
Jim
But, do understand, it is perfectly normal to have some amount of dripping solder paste falling off the bottom of the leads, because when you print over the hole with a paste process, then insert your part, you're going to knock some small volume of paste onto the pin, and some of that is bound to fall off. You just need to make sure that it's not degrading the integrity of your final joints.
Phil
The only other thing I want to add is this applies to both reflow ovens and vapor phase. Beyond that, this is Phil Zarrow and Jim Hall.
Jim
Saying whatever you do, don't solder like my brother.
Phil
Right. And, again, regardless of whether you're using wave, reflow, vapor phase or hand soldering, don't solder like my brother either.
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